Process for sweetening of LPG, light petroleum distillates by liquid-liquid extraction using metal phthalocyanine sulphonamide catalyst

ABSTRACT

The present invention related to a process for sweetening of LPG light petroleum distillates by liquid liquid extraction using metal phtalocyanine sulphonamide catalyst which comprises extracting the mercaptanes contain in LPG, light petroleum distillate like pentanes, light straight run naphtha by liquid-liquid extraction using an aqueous or alcoholic solution of alkali metal hydroxide of concentration ranging between 1 wt % to 50 wt % in the presence of a metal phthalocyanine sulphonamide catalyst in the concentration ranging from 5-4000 ppmw, at a temperature ranging from 10° C. to 80° C. at a pressure ranging from 1 kg/cm 2 -50 kg/cm 2  in a continuous or batch manner, converting the mercaptanes present in above said extract into corresponding disulphides by passing air, oxygen or any oxygen containing gas at the above same temperature and pressure, regenerating the alkali solution containing catalyst for recycling by separating the upper layer of disulphides from said alkali solution of catalyst.

The present invention relates to a process for sweetening of LPG, lightpetroleum distillates by liquid-liquid extraction using metalphthalocyanine sulphonamide catalyst.

Particularly, the invention relates to a process for sweetening of LPG,light petroleum distillates like pentanes, light straight run naphtha(LSRN), comprising of liquid-liquid extraction of the mercaptanscontained therein by alkali solution and regeneration of the mercaptancontaining alkali solution by oxygen using metal phthalocyaninesulphonamide catalyst, whereby the mercaptans are converted tocorresponding disulphides and the regenerated alkali solution can bereused for mercaptan extraction.

Metal phthalocyanine sulphonamide catalyst has been prepared by aprocedure as discussed and described in our co-pending Indian PatentApplication No 1032/DEL/2000 corresponding to U.S. patent applicationSer. No. 09/804,994.

It is known that the presence of mercaptans in the petroleum productslike LPG, naphtha, gasoline, kerosene, ATF etc is highly undesirable dueto their foul odour and highly corrosive nature. These are alsopoisonous to the catalysts and adversely affect the performance oftetraethyl lead as octane booster. Although there are several processesknown for the removal of mercaptans from petroleum products, the mostcommon practice is to oxidize the mercaptans present, to lessdeleterious disulphides with air in the presence of a catalyst.Generally, the lower mercaptans present in LPG, pentanes, LSRN and lightthermally cracked naphtha are first extracted in alkali solution andthen oxidized to disulphides with air in the presence of a catalyst. Thedisulphides, being insoluble in alkali solution is separated out fromthe top and the alkali is regenerated. In the liquid-liquid sweeteningthe lower mercaptans present in petroleum products like pentanes. LSRN,FCC cracked naphtha etc. are converted to disulphides by directoxidation with air in the presence of alkali solution and catalyst. Thehigher molecular weight mercaptans present in petroleum products likeheavy naphtha, FCC gasoline, ATF and kerosene are oxidized todisulphides with air in a fixed bed reactor containing catalystimpregnated on a suitable support like activated carbon (Catal. Rev.Sci. Eng. 35(4), 571-609, 1993).

It is also well known that the phthalocyanines of the metals likecobalt, iron, manganese, molybdenum and vanadium catalyze the oxidationof mercaptans to disulphides in alkaline medium. Among these cobalt andvanadium phthalocyanines are preferred. As the metal phthalocyanines arenot soluble in aqueous medium, for improved catalytic activity theirderivatives like sulphonated and carboxylated metal phthalocyanines areused as catalyst for sweetening of petroleum fractions. For example useof cobalt phthalocyanine monosulphonate as the catalyst in the fixed bedsweetening of various petroleum products (U.S. Pat. Nos. 3,371,031;4,009,120; 4,207,173; 4,028,269; 4,087,378; 4,141,819; 4,121,998;4,124,494; 4,124,531) and cobalt phthalocyanine disulphoante (U.S. Pat.No. 4,250,022) tetra sulphonate (U.S. Pat. No. 2,622,763) and themixture thereof (U.S. Pat. No. 4,248,694) as catalysts for liquid-liquidsweetening and alkali regeneration in mercaptan extraction of lightpetroleum distillates has been reported. The use of phenoxy substitutedcobalt phthalocyanine as sweetening catalyst (Ger Offen 3,816,952),cobalt and vanadium chelates of 2, 9, 16, 23-tetrakis(3,4-dicarboxybenzoyl) phthalocyanine as effective catalyst for bothhomogeneous and fixed bed mercaptan oxidation (Ger Offen 2,757,476; Fr.Demande 2,375,201) and cobalt, vanadium chelates oftetrapyridinoporphyrazine as active catalysts for sweetening of sourpetroleum distillates (Ger Offen 2,441,648) has also been reported.

It is well known that the catalysts used for the sweetening of LPG andlight petroleum distillates like pentanes, LSRN etc. by liquid-liquidmercaptan extraction and alkali regeneration are di-, tri- and tetrasulphonates of metal phthalocyanines particularly those of cobalt andvanadium phthalocyanines; cobalt phthalocyanine sulphonates beingspecially preferred. The cobalt phthalocyanine sulphonates, differ inactivity and in their solubility characteristics depending upon thenumber of sulphonate functionalities leading to problems in their use ascatalysts.

Cobalt phthalocyanine disulphonate a commonly used catalyst insweetening of LPG and light petroleum fractions by liquid-liquidmercaptan extraction and alkali regeneration is extremely dusty in thedry fine powder form and causes handling problem. To overcome thisproblem cobalt phthalocyanine disulphonate is admixed with water andcommonly used as a slurry. However, with insufficient mixing the cobaltphthalocyanine disulphonate precipitates out from the slurry. Moreover,even if the slurry is mixed sufficiently, it retains the cobaltphthalocyanine disulphonate in suspension for a particular length oftime only, beyond which the slurry becomes extremely viscous and mayform gel, making it very difficult to remove the material frompackaging. Cobalt phthalocyanine tetrasulphonate, on the other hand, ishighly soluble in water and its use can eliminate precipitation and gelforming problems associated with the use of cobalt phthalocyaninedisulphonate. However, it is reported that cobalt phthalocyaninetetrasulphonate has lower catalytic activity than cobalt phthalocyaninedisulphonate (U.S. Pat. No. 4,885,268).

In one of our applications 1032/Del/2000 corresponding to U.S. patentapplication Ser. No. 09/804,994, we reported an improved process for thepreparation of metal phthalocyanine sulphonamide catalyst useful forsweetening and obviates the drawback as detailed above.

The main objective of the present invention is to provide a process forsweetening of LPG, light petroleum distillates by liquid-liquidextraction and alkali regeneration using metal phthalocyaninesulphonamide catalyst, which obviates the drawbacks as detailed above.

Accordingly the present invention provides a process for sweetening ofLPG, light petroleum distillates by liquid-liquid extraction using metalphthalocyanine sulphonamide catalyst which comprises extracting themercaptanes contained in LPG, light petroleum distillate like pentanes,light straight run naphtha by liquid-liquid extraction using an aqueousor alcoholic solution of alkali metal hydroxide of concentration rangingbetween 1 wt % to 50 wt % in the presence of a metal phthalocyaninesulphonamide catalyst in the concentration ranging from 5-4000 ppmw, ata temperature ranging from 10° C. to 80° C., at a pressure ranging from1 kg/cm²-50 kg/cm² in a continuous or batch manner, converting themercaptanes present in above said extract into corresponding disulphidesby passing air, oxygen or any oxygen containing gas at the above sametemperature and pressure, regenerating the alkali solution containingcatalyst for recycling by separating the upper layer of disulphides fromsaid alkali solution of catalyst.

In an embodiment of the present invention metal phthalocyaninesulphonamide catalyst used in selected from the group consisting ofcobalt, manganese, nickel, iron, vanadium phthalocyanine sulphonamideand their N-substituted sulphonamide derivatives most preferably cobaltphthalocyanine sulphonamide.

In an embodiment of the present invention the alkali solution used formercaptan extraction is selected from aqueous or alcoholic solution ofalkali metal hydroxides selected from the group consisting of sodiumhydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide,and cesium hydroxide most preferably aqueous solution of sodium andpotassium hydroxide.

In yet another embodiment of the present invention the concentration ofthe alkali solution used is preferably in the range 7% to 25% by weight.

In yet another embodiment of the present invention the metalphthalocyanine sulphonamide catalyst used is preferably in theconcentration ranging between 10 to 1000 ppmw related to alkalinereagent.

In yet another embodiment of the present invention the conversion ofmercaptanes to disulphides is effected preferably at 35° C. to 60° C.

In yet another embodiment of the present invention the conversion ofmercaptanes to disulphides is effected preferably at 1 kg/cm² to 15kg/cm² pressure.

In yet another embodiment of the present invention the conversion ofmercaptanes to disulphides is preferably effected by air.

In still another embodiment of the present invention the regeneration ofalkali solution is effected with the mercaptide sulphur ranking from 10ppmw to 40,000 ppmw in feed stocks.

Process Description

In the sweetening process herein contemplated the undesirable mercaptanscontained in LPG and light petroleum distillates like, pentanes, LSRNare extracted with alkali solution containing metal phthalocyaninesulphonamide catalyst through a counter current liquid-liquidextraction. The sweetened petroleum distillate is then passed through analkali settler and sand filter to remove entrained alkali. Themercaptans and catalyst containing alkali solution obtained from theextractor is oxidized by oxygen or oxygen containing gas like air in onoxidizer whereby the mercaptans present in alkali solution are convertedinto corresponding disulphides and alkali is regenerated. The disulphideoil being insoluble separates from alkali solution as upper layer and isdrained. The regenerated alkali solution is reused for mercaptanextraction.

In the sweetening process with this catalyst system extraction ofmercaptans from light petroleum distillates can be effected at 10° C. to80° C. but the preferred range is 10° C. to 40° C. The extraction can beeffected at a pressure from ambient to 50 kg/cm² or more with thepreferable pressure range ambient to 20 kg/cm². The alkali solution usedin the extraction is aqueous/alcoholic solution of alkali metalhydroxide such as sodium hydroxide, potassium hydroxide, lithiumhydroxide, rubidium hydroxide, cesium hydroxide, aqueous solution ofsodium hydroxide and potassium hydroxide being preferred. Theconcentration of the alkali solution used is 1% to 50% the preferredrange being 7 to 25%.

The sweetening process is effected with the metal phthalocyaninesulphonamide catalyst like cobalt, manganese, nickel, iron and vanadiumphthalocyanine sulphonamide and their N-substituted derivatives, thepreferred catalyst is cobalt phthalocyanine sulphonamide. The catalystis used in the concentration 1 to 1000 ppmw related to alkali solution,the preferred range is 10-1000 ppmw.

The regeneration of mercaptans containing alkali solution with metalphthalocyanine sulphonamide catalyst is effected at ambient to 90° C.temperature. The preferred range being 35° C. to 60° C.

The regeneration of alkali solution is effected at atmosphere to 50Kg/cm² pressure, the preferred range being 1-15 Kg/cm².

The regeneration of alkali solution is effected by air, oxygen or anyother oxygen containing gas, air being especially preferred.

The following examples are given by way of illustration and thereforeshould not be construed to limit the scope of the invention.

EXAMPLE 1 Preparation of Cobalt Phthalocyanine Sulphonamide Catalyst asDescribe in our Patent Application No. 1032/del/2000 Preparation ofCobalt Phthalocyanine Sulphonyl Chloride

For the preparation of cobalt phthalocyanine sulphonyl chloride, 30parts by weight of cobalt phthalocyanine were slowly added with stirringto 315 parts by weight of chlorosulphonic acid. The reaction mixture washeated to about 75° C. in one hour and from 75° C. to about 130° C. in1.5 hours by controlling the heating rate, with constant stirring. Thereaction mixture, after maintaining 130-135° C. for additional 4 hours,was cooled to 60-65° C., and then 123 parts of thionyl chloride wereslowly added. The whole contents were heated to 79° C. and maintained atthis temperature for one hour. The reaction product was cooled to roomtemperature and slowly added to crushed ice, keeping the temperaturepreferably below 5° C. The precipitated cobalt phthalocyanine sulphonylchloride was filtered and washed thoroughly with cold water. Thefiltered cake was stored wet at 0° C. till further processing.

Preparation of Cobalt Phthalocyanine Sulphonamide

In a typical preparation of cobalt phthalocyanine sulphonamides, totalwet cake of cobalt phthalocyanine sulphonyl chloride, obtained wasdispersed in 900 parts of ice water and 190 parts of methanol added toget homogeneous dispersion. The reaction mixture was stirred at 5-8° C.and ammonia gas was passed till the mixture was fairly alkaline (pH8-9). Pyridine (1.2 parts) was then added and the mixture stirred atroom temperature for 20 minutes. This was followed by addition of 6parts of 10% sodium hydroxide solution followed by stirring the reactionmixture for 40 minutes at room temperature. The contents were thenheated to 80° C. and after maintaining at this temperature for 1 hour,cooled to room temperature and poured over a mixture of ice andconcentrated hydrochloric acid keeping the pH fairly acidic (2-3). Theprecipitated cobalt phthalocyanine tetrasulphonamide was filtered,washed thoroughly with cold water and dried in vacuum oven to yield 44gms of the product. The FAB mass spectral analysis of the sulphonamideobtained using cobalt phthalocyanine as the starting material showed thepresence of tetra sulphonamide as the major isomer, followed bytrisulphonamide and disulphonamide isomers.

EXAMPLE 2 Alkali Regeneration in LPG Mercaptan Extraction

As the metal phthalocyanine sulphonamide catalyst has no effect inmercaptan extraction from LPG and it only catalyze the oxidation ofmercaptide to disulphide to regenerate the caustic being used forextraction, the experiments were designed to study caustic regenerationby using ethane thiol mercaptan as the model mercaptan.

In the model experiments the calculated amount of ethyl mercaptan wasadded to light naphtha. Its mercaptan sulphur content was estimated byUOP method 163-89. Thus prepared feed was taken in a round bottom flask.The mercaptan present in naphtha was extracted with 14% aqueous sodiumhydroxide solution containing 200 ppmw of the catalyst with stirringunder inert atmosphere. After extraction the mercaptan sulphur contentof naphtha was estimated. The spent alkali thus obtained, wasregenerated by passing air into it. The alkali regeneration time (asindicated by reappearance of the blue colour in the solution) wasmonitored in the repeated experiments by reusing the same catalystsolution. The strength of the sodium hydroxide solution was alsomonitored. The mercaptide sulphur content of the regenerated sodiumhydroxide solution was found to be below 1 ppmw by above method (UOP163-89) throughout the entire study showing complete alkaliregeneration. Results are given in Table-1.

TABLE 1 Mercaptan sulphur in feed, ‘S’ppmw 1500 Catalyst concentrationin alkali ppmw  200 Volume of alkali taken for extraction  50 ml Volumeof Mercaptan in feed Commutative extracted Alkali NaSR in treated withvolume of feed feed regeneration regenerated alkali ml treated ml ‘S’ppmw time, min. alkali ppmw 300 300 <5 10.5 <1 300 600 <5 12.0 <1 300900 <5 12.0 <1 300 1200 <5 12.5 <1 300 1500 <5 15.0 <1 150 1650 <5 12.0<1

EXAMPLE 3 Alkali Regeneration in LPG Mercaptan Extraction in GlassColumn

As the metal phthalocyanine sulphonamide catalyst has no effect inmercaptan extraction from LPG and it only catalyze the oxidation ofmercaptide to disulphide to regenerate the alkali solution used forextraction, experiments were designed to study caustic regeneration byusing ethane thiol as the model mercaptan. The laboratory experimentalset-up consist of a glass column with air inlet at the bottom connectedto air cylinder through control valve. Calculated amount of ethane thiolwas added to 14% aqueous sodium hydroxide containing 200 ppmw metalphthalocyanine sulphonamide catalyst and its mercaptan sulphur contentwas estimated by UOP method 163-89. The mixture was then transferred tothe glass column and oxidized by passing air till all the ethylmercaptide was converted to disulphide indicated by the appearance ofblue colour. Thus formed diethyl disulphide clearly separated fromcatalyst containing alkali solution in the upper layer. The conversionof mercaptide to disulphide was monitored by analyzing the mercaptideconcentration in the reaction mixture at different intervals. Theresults are given in Table-2.

TABLE 2 Mercaptan sulphur in 14% sodium hydroxide solution ppmw 3307Concentration of the catalyst in alkali solution ppmw  200 Total volumeof reaction mixture, taken ml  230 Air rate, lit/min   0.8 Time, minMercaptan ‘S’, Conversion, wt % 0 3307 0 1 2816 14.85 5 45 98.64 8 0100.00

EXAMPLE 4 Alkali Regeneration in LPG Mercaptan Extraction in GlassColumn

Procedure followed and experimental details were same as given inExample 3. The results obtained are presented in Table-3.

TABLE 3 Mercaptan sulphur in 14 % sodium hydroxide solution ppmw 8533Concentration of the catalyst in alkali solution ppmw  200 Total volumeof reaction mixture, taken ml  230 Air rate, lit/min   0.83 Time, minMercaptan ‘S’ ppmw Conversion, wt % 0 8533 0 1 6220 27.11 5 5042 40.9110 1833 78.52 15 0 100.00

EXAMPLE 5 Alkali Regeneration in LPG Mercaptan Extraction in GlassColumn

Procedure followed and experimental details were same as given inExample 3. Thus obtained are presented in Table-4.

TABLE 4 Mercaptan sulphur in 14% solution hydroxide solution ppmw 13129Concentration of the catalyst in alkali solution ppmw  200 Total volumeof reaction mixture, taken ml  230 Air rate, lit/min   0.8 Time, minMercaptan ‘S’ ppmw Conversion, wt % 0 13129 0 1 12251 6.69 10 7337 44.1220 1101 91.61 25 0 100.00

EXAMPLE 6 Alkali Regeneration in LPG Mercaptan Extraction in GlassColumn

Procedure followed and experimental details were same as given inExample 3. The results obtained are presented in Table-5.

TABLE 5 Mercaptan sulphur in 14% sodium hydroxide solution ppmw 17626Concentration of the catalyst in alkali solution ppmw  200 Total volumeof reaction mixture, taken ml  230 Air rate, lit/min   0.075 Time, minMercaptan ‘S’ ppmw Conversion, wt % 0 17626 0 1 16663 5.46 10 8140 53.8220 1664 90.56 29 0 100.00

We claim:
 1. A process for sweetening of LPG, light petroleumdistillates by liquid-liquid extraction using metal phthalocyaninesulphonamide catalyst which comprises the steps of: extracting themercaptans contained in LPG, light petroleum distillate or lightstraight run naphtha by liquid-liquid extraction using an aqueous oralcoholic solution of alkali metal hydroxide of disulphides by usingair.
 2. A process as claimed in claim 1, wherein metal phtalocyaninesulphonamide catalyst used is selected from the group consisting ofcobalt, manganese, nickel, iron, vanadium phthalocyanine sulphonamideand their N-substituted sulphonamide derivatives most preferably cobaltphthalocyanine sulphonamide.
 3. A process as claimed in claim 1, whereinthe alkali solution used for mercaptan extraction is selected fromaqueous or alcoholic solution of alkali metal hydroxide selected fromthe group consisting of sodium hydroxide, potassium hydroxide, lithiumhydroxide, rubidium hydroxide and cesium hydroxide most preferablyaqueous solution of sodium and potassium hydroxide.
 4. A process asclaimed in claim 1, wherein concentration of the alkali solution used ispreferably in the range 7% to 25% by weight.
 5. A process as claimed inclaim 1, wherein the metal phthalocyanine sulphonamide catalyst used ispreferably in the concentration ranging between 10 to 1000 ppmw relatedto alkaline reagent.
 6. A process as claimed in claim 1, wherein theconversion of mercaptanes to disulphides is effected preferably at 35°C. to 60° C.
 7. A process as claimed in claim 1, wherein the conversionof mercaptanes to disulphides is effected preferably at 1 kg/cm² to 15kg/cm² pressure.
 8. A process as claimed in claim 1, wherein theconversion of mercaptanes to disulphides is preferably effected by air.9. The process as claimed in claim 1, wherein the regeneration of thesolution is effected with a feed stock containing sulphur in an amountranging from 10 ppmw to 40,000 ppmw.
 10. The process as claimed in claim2, wherein the alkali solution used for mercaptan extraction is selectedfrom aqueous or alcoholic solution of alkali metal hydroxide selectedfrom the group consisting of sodium hydroxide, potassium hydroxide,lithium hydroxide, rubidium hydroxide and cesium hydroxide.
 11. Theprocess as claimed in claim 2, wherein concentration of the alkalisolution used is in the range 7% to 25% by weight.
 12. The process asclaimed in claim 3, wherein concentration of the alkali solution used isin the range 7% to 25% by weight.
 13. The process as claimed in claim 2,wherein the metal phthalocyanine sulphonamide catalyst used is in theconcentration ranging between 10 to 1000 ppmw related to alkalinereagent.
 14. The process as claimed in claim 3, wherein the metalphthalocyanine sulphonamide catalyst used is in the concentrationranging between 10 to 1000 ppmw related to alkaline reagent.
 15. Theprocess as claimed in claim 4, wherein the metal phthalocyaninesulphonamide catalyst used is in the concentration ranging between 10 to1000 ppmw related to alkaline reagent.
 16. The process as claimed inclaim 2, wherein the conversion of mercaptans to disulphides is effectedat 35° C. to 60° C.
 17. The process as claimed in claim 3, wherein theconversion of mercaptans to disulphides is effected at 35° C. to 60° C.18. The process as claimed in claim 4, wherein the conversion ofmercaptans to disulphides is effected at 35° C. to 60° C.
 19. Theprocess as claimed in claim 5, wherein the conversion of mercaptans todisulphides is effected at 35° C. to 60° C.
 20. The process according toclaim 1 wherein the metal phthalocyanine sulphonamide catalyst is cobaltphthalocyanine sulphonamide.
 21. The process as claimed in claim 1wherein the solution of alkali metal hydroxide is an aqueous solution ofsodium and potassium hydroxide.
 22. The process as claimed in claim 2wherein the solution of alkali metal hydroxide is an aqueous solution ofsodium and potassium hydroxide.